Extracellular nucleotides regulate many biological processes by selectively activating cell surface receptors. Nucleotides within the liquid film lining the airway epithelia control the mucociliary clearance process that removes inhaled noxious materials. In addition, they can activate inflammatory cells that migrate into diseased airways. Therefore, understanding the mechanism(s) of nucleotide release into the airways has important therapeutic implications. ATP, UTP, UDP and adenosine activate a subset of P2Y and A2b receptors that regulate ion secretion, increase ciliary beat frequency and promote mucin secretion. It is still largely unknown how nucleotides reach the airway surfaces to accomplish extracellular signaling. Circumstantial evidence exists for both plasma membrane channels that allow efflux of cytosolic nucleotides and for the involvement of vesicular secretory pathway(s). Whether nucleotide release is conductive, vesicular or both is not unambiguously known. We have discovered that UDP-sugars are released into ASL of well-differentiated primary human airway epithelia in addition to ATP, and that enhanced secretion of mucins by cultured goblet-like cells is accompanied by enhanced release of UDP-glucose and ATP. We have also discovered that UDP-glucose is a potent neutrophil chemoattractant. Therefore, we hypothesize that nucleotide release by goblet cells encompasses an exocytotic component associated with mucin secretion, and that this pathway likely is a major contributor of nucleotides and nucleotide-sugars that play physiological roles in the airways. Since UDP-sugars are substrates of glycosylation reactions in the ER and Golgi lumen in all mammalian cells, we also propose that apical export of glycoconjugates provides a mechanism of nucleotide release by non-goblet cells. A research plan to assess the contributions of secretory pathways in airway epithelia nucleotide release is delineated below. This plan takes advantage of unique methodologies developed by our group to quantity all naturally occurring nucleotide species with nanomolar sensitivity. Delineation of nucleotide-releasing mechanisms will provide new possibilities to improve MCC function in chronic lung diseases characterized by mucin-obstructed and inflamed airways. [unreadable] [unreadable]